The present invention pertains to a frequency up/down converter.
Frequency up/down converters (referred to below as up/down converters) are known as a technology for frequency conversion. FIG. 1 shows a diagram of a conventional up converter and FIG. 2 shows a diagram of a conventional down converter.
First, a conventional up converter will be described while referring to FIG. 1. First local oscillator LO1124 of the up converter in FIG. 1 is typically a low phase-noise signal source of a fixed frequency and second local oscillator LO2126 is a low phase-noise signal source of a variable frequency. In FIG. 1, signals given to input terminal 110 are passed through BPF (band pass filter) 112 and mixed with signals from LO1124 (of a predetermined fixed frequency) by mixer 114 and the frequency component of the difference between the two signals is removed, that is, the frequency component of the sum of the two signals, is produced by BPF 116. There is further mixing with signals output at a predetermined frequency from LO2126 by mixer 118 and the frequency component of the sum of the two signals is removed by LPF (low pass filter) 120 and output to output terminal 122.
In this case, assuming that signal f110 given to input terminal 110 is
f110=cos(wxe2x80x94if*t)xe2x80x83xe2x80x83(1)
as a signal without phase noise, signal f124 output from LO1 is
f124=cos(w2*t+xcex8pn2(t))xe2x80x83xe2x80x83(2)
with phase noise as xcex8pn2(t), and signal f126 from LO2 is
xe2x80x83f126=cos(w3*t+xcex8pn3(t))xe2x80x83xe2x80x83(3)
with phase noise as xcex8pn3(t), first intermediate frequency signal IF1 at the output of mixer 114 is the product of both signals f110 and f124. To summarize,                                                         IF1              =                              xe2x80x83                            ⁢                                                cos                  ⁡                                      (                                          w_if                      *                      t                                        )                                                  *                                  cos                  ⁡                                      (                                                                  w2                        *                        t                                            +                                              θ                        ⁢                                                  xe2x80x83                                                ⁢                                                  pn2                          ⁡                                                      (                            t                            )                                                                                                                )                                                                                                                          =                              xe2x80x83                            ⁢                              (                                                      cos                    ⁡                                          (                                                                                                    (                                                          w_if                              +                              w2                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn2                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        +                                                                                                                                          xe2x80x83                                ⁢                                                      cos                    ⁡                                          (                                                                                                    (                                                          w_if                              -                              w2                                                        )                                                    *                          t                                                -                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn2                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        )                                            /              2                                                          (        4        )            
Furthermore, in this specification, the formulas representing signals that have passed through mixers or filters focus on the relationship with frequency for what needs explanation, but persons skilled in the art can alter the formulas as needed for amplitude, and therefore, the details are not given special mention. Therefore, the phrase xe2x80x9cto summarizexe2x80x9d has been used when the formulas are introduced.
Next, the lower frequency components are removed by BPF 116, and therefore, signal f116 at the output of BPF 116 becomes
f116=cos((wxe2x80x94if+w2)*t+xcex8pn2(t))xe2x80x83xe2x80x83(5)
When frequency is converted by mixer 118, second intermediate frequency signal IF2 at the output of mixer 118 becomes                                                         IF2              =                              xe2x80x83                            ⁢                                                cos                  ⁡                                      (                                                                  w3                        *                        t                                            +                                              θ                        ⁢                                                  xe2x80x83                                                ⁢                                                  pn3                          ⁡                                                      (                            t                            )                                                                                                                )                                                  *                                  cos                  ⁡                                      (                                                                                            (                                                      w_if                            +                            w2                                                    )                                                *                        t                                            +                                              θ                        ⁢                                                  xe2x80x83                                                ⁢                                                  pn2                          ⁡                                                      (                            t                            )                                                                                                                )                                                                                                                          =                              xe2x80x83                            ⁢                              (                                                      cos                    ⁡                                          (                                                                                                    (                                                          w3                              +                              w_if                              +                              w2                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn3                            ⁡                                                          (                              t                              )                                                                                                      +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn2                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        +                                                                                                                                          xe2x80x83                                ⁢                                                      cos                    ⁡                                          (                                                                                                    (                                                          w3                              -                              w_if                              -                              w2                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn3                            ⁡                                                          (                              t                              )                                                                                                      -                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        )                                            /              2                                                          (        6        )            
The higher frequency components are removed by LPF 120 here, and therefore, signal f120 at the output of LPF 120 becomes
f120=cos((w3xe2x88x92wxe2x80x94ifxe2x88x92w2)*t+xcex8pn3(t)xe2x88x92xcex8pn2(t))xe2x80x83xe2x80x83(7)
In formula (7), since xcex8pn3(t) and xcex8pn2(t) are non-correlated noise from different signal sources, these phase noises are added to the signal f120 to output terminal 122 and given to output. The results relating to phase noise here would not be different, if the component of lower frequency from first intermediate frequency IF1 was used.
Next, a conventional down converter will be described while referring to FIG. 2. First local oscillator LO1226 of the down converter in FIG. 2 is a low phase-noise signal source of variable frequency and second local oscillator LO2224 is a low phase-noise signal source of fixed frequency. The signal given to input terminal 222 passes through LPF 220 in FIG. 2 in order to remove images of frequency components and is mixed with a signal of a predetermined frequency from first local oscillator LO1226 by mixer 218. The frequency component of the sum of both signals is removed by BPF 216, and further mixing with signals (of a predetermined fixed frequency) from second local oscillator LO2224 is performed by mixer 214. The frequency component of the sum of the two signals is removed by BPF 212 and, then the result is output to output terminal 210.
In this case, assuming that input signal f222 of input terminal 222 is
f222=cos(wxe2x80x94in*t)xe2x80x83xe2x80x83(8)
as a signal without phase noise, signal f226 from first local oscillator LO1 is
f226=cos(w1*t+xcex8pn1(t))xe2x80x83xe2x80x83(9)
with phase noise as xcex8pn1(t), and signal f224 from second local oscillator LO2224 is
f224=cos(w2*t+xcex8pn2(t))xe2x80x83xe2x80x83(10)
with phase noise as xcex8pn2(t), first intermediate frequency signal IF1 at the output of mixer 218 becomes the product of input signal f222 and signal f226 from LO1 and                                                         IF1              =                              xe2x80x83                            ⁢                                                cos                  ⁡                                      (                                                                  w1                        *                        t                                            +                                              θ                        ⁢                                                  xe2x80x83                                                ⁢                                                  pn1                          ⁡                                                      (                            t                            )                                                                                                                )                                                  *                                  cos                  ⁡                                      (                                          w_in                      *                      t                                        )                                                                                                                          =                              xe2x80x83                            ⁢                              (                                                      cos                    ⁡                                          (                                                                                                    (                                                          w1                              +                              w_in                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn1                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        +                                                                                                                                          xe2x80x83                                ⁢                                                      cos                    ⁡                                          (                                                                                                    (                                                          w1                              -                              w_in                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn1                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        )                                            /              2                                                          (        11        )            
Here, the higher component is removed by BPF 216 and therefore, signal f216 at the output of BPF216 becomes
f216=cos((w1xe2x88x92wxe2x80x94in)*t+xcex8pn1(t))xe2x80x83xe2x80x83(12)
Next, when frequency is converted by mixer 214, second intermediate frequency signal IF2 at the output of mixer 214 becomes                                                         IF2              =                              xe2x80x83                            ⁢                                                cos                  ⁡                                      (                                                                                            (                                                      w1                            -                            w_in                                                    )                                                *                        t                                            +                                              θ                        ⁢                                                  xe2x80x83                                                ⁢                                                  pn1                          ⁡                                                      (                            t                            )                                                                                                                )                                                  *                                  cos                  ⁡                                      (                                                                  w2                        *                        t                                            +                                              θ                        ⁢                                                  xe2x80x83                                                ⁢                                                  pn2                          ⁡                                                      (                            t                            )                                                                                                                )                                                                                                                          =                              xe2x80x83                            ⁢                              (                                                      cos                    ⁡                                          (                                                                                                    (                                                          w1                              -                              w_in                              +                              w2                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn1                            ⁡                                                          (                              t                              )                                                                                                      +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn2                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        +                                                                                                                                          xe2x80x83                                ⁢                                                      cos                    ⁡                                          (                                                                                                    (                                                          w1                              -                              w_in                              -                              w2                                                        )                                                    *                          t                                                +                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn1                            ⁡                                                          (                              t                              )                                                                                                      -                                                  θ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      pn2                            ⁡                                                          (                              t                              )                                                                                                                          )                                                        )                                            /              2                                                          (        13        )            
and when the higher component is dropped by BPF 212, signal f212 at the output of BPF 212 becomes
f212=cos((w1xe2x88x92wxe2x80x94inxe2x88x92w2)*t+xcex8pn1(t)xe2x88x92xcex8pn2(t))xe2x80x83xe2x80x83(14)
In formula (14), since xcex8pn3(t) and xcex8pn2(t) are non-correlated noise from different signal sources, these phase noises are added to output signals and are given to output.
Accordingly, there is a disadvantage with conventional up/down converters in that phase noise from internal signal sources is obtained in the output and it becomes necessary to use a high-performance internal signal source with low phase-noise in order to keep phase noise to lower.
In particular, signal sources 124 and 224 of fixed frequency in conventional up/down converters must have as high an output frequency as signal sources 126 and 226 of variable frequency. In general, as higher the output frequency becomes in a signal source, the phase noise level also increases. Therefore, a signal source with low phase-noise is needed, even when used as the signal source of fixed frequency, and as a result, the up/down converter becomes expensive.
Therefore, when this type of conventional converter is used in systems such as IC testers, etc., the cost of developing a dedicated fixed frequency signal source increases and becomes expensive. Moreover, output frequency cannot be varied, and therefore, this signal source cannot be flexibly used with other modules. Consequently, the problems with these conventional converters are two-fold.
Therefore, there was a need for a high-frequency up/down converter with which phase noise is reduced even if a low-cost ordinary signal source is used.
In order to solve the abovementioned problems, the purpose of the present invention is to present an up/down converter with which phase noise is reduced, even when an ordinary signal source is employed.
Another purpose of the present invention is to present a low-cost device or method for presenting a high-frequency up/down converter with low phase-noise.
In order to accomplish this purpose, in the first aspect of the present invention there is provided an up converter comprising: a first local oscillator; a first mixer means for mixing input signals and signals from the first local oscillator and producing a frequency component of the sum of the two frequency signals; a second local oscillator; a second mixer means for mixing the signals from the first local oscillator and the second local oscillator and producing the frequency component of the sum of the two; and a third mixer means for mixing the signals from the first and second mixer means and producing the frequency component of the difference between the two signals.
In order to accomplish this purpose, in the second aspect of the present invention, the up converter according to the first aspect of the invention, further comprises a power splitter connected to the first local oscillator for splitting signals and feeding signals to the first and the second mixer means.
In order to accomplish this purpose, in the third aspect of the present invention, the up converter according to the first aspect of the invention, further comprises a first amplifier between the second and the third mixer means.
In order to accomplish this goal, in the fourth aspect of the present invention, an up converter comprises: a first local oscillator; a power splitter connected to the first local oscillator for splitting signals, a first mixer connected to one of outputs from the power splitter and input signals for mixing the signals from both; a first filter connected to the first mixer for removing the frequency component of the difference between two frequencies of the signals that have been input to the first mixer; a second local oscillator; a second mixer connected to the second local oscillator and another output from the power splitter for mixing the signals from both; a second filter connected to the second mixer for removing the frequency component of the difference between the signals that have been input to the second mixer; a third mixer connected to the first and second filters for mixing the signals from the two filters; and a third filter connected to the third mixer for removing the frequency component of the sum of two frequencies of the signals that have been input to the third mixer.
In order to accomplish this purpose, in the fifth aspect of the present invention, the up converter according to the fourth aspect of the invention, further comprises a first amplifier between the second filter and the third mixer.
In order to accomplish this purpose, in the sixth aspect of the present invention, the up converter according to the second aspect of the invention, further comprises: a second amplifier between the power splitter and the first mixer; and a third amplifier between the power splitter and the second mixer.
In order to accomplish this purpose, in the seventh aspect of the present invention, the up converter according to the sixth aspect of the invention, further comprises a delay element between the power splitter and the third amplifier.
In order to accomplish this purpose, in the eighth aspect of the present invention, the up converter according to the sixth aspect of the invention, further comprises a delay element between the third amplifier and the second mixer.
In order to accomplish this purpose, in the ninth aspect of the present invention, in the up converter according to the first aspect of the invention, the first local oscillator is a fixed-frequency oscillator and the second local oscillator is a variable-frequency oscillator.
In order to accomplish this purpose, in the tenth aspect of the present invention, a down converter comprises: a first local oscillator; a second local oscillator; a first mixer means for mixing the signals from the second local oscillator with the signals from the first local oscillator and producing the frequency component of the sum of the two; an input terminal; a second mixer means for mixing the signals from the input terminal and the signals from the first mixer means and producing the frequency component of the difference between the two; and a third mixer means for mixing the signals from the first local oscillator and the signals from the second mixer means and producing the frequency component of the difference between the two.
In order to accomplish this purpose, in the eleventh aspect of the present invention, the down converter according to the tenth aspect of the invention, further comprises a power splitter connected to the first local oscillator for splitting signals and feeding signals to the first and the third mixer means.
In order to accomplish this purpose, in the twelfth aspect of the present invention, the down converter according to the tenth aspect of the invention, further comprises a fourth filter connected between the input terminal and the second mixer means for producing a component within a predetermined frequency range of the signals from the input terminal.
In order to accomplish this purpose, in the thirteenth aspect of the present invention, the down converter according to the tenth aspect of the invention, further comprises a first amplifier between the first mixer and second mixer.
In order to accomplish this purpose, in the fourteenth aspect of the present invention, a down converter comprises: a first local oscillator; a power splitter connected to the output of the first local oscillator for splitting signals; a second local oscillator; a first mixer connected with the second local oscillator and an output from the power splitter for mixing the two signals; a first filter connected with the first mixer for removing the frequency component of the difference between signals that have been input to the first mixer; an input terminal; a second mixer connected to the input terminal and the first filter for mixing signals from both; a second filter connected to the second mixer for removing the frequency component of the sum of signals input to the second mixer; a third mixer connected t o another output from the power splitter and the second filter for mixing the signals from the two; and a third filter connected to the third mixer for removing the frequency component of the sum of signals input to the third mixer
In order to accomplish this purpose, in the fifteenth aspect of the present invention, the down converter according to the fourteenth aspect of the invention, further comprises a fourth filter for producing the component within a predetermined frequency range of signals from the input terminal between the input terminal and the second mixer.
In order to accomplish this purpose, in the sixteenth aspect of the present invention, the down converter according to the fourteenth aspect of the invention, further comprises a first amplifier between the first filter and the second mixer.
In order to accomplish this purpose, in the seventeenth aspect of the present invention, the down converter according to the eleventh aspect of the invention, further comprises: a second amplifier between the power splitter and the first mixer; and a third amplifier between the power splitter and the third mixer.
In order to accomplish this purpose, in the eighteenth aspect of the present invention, the down converter according to the seventeenth aspect of the invention, further comprises a delay element between the power splitter and the third amplifier.
In order to accomplish this purpose, in the nineteenth aspect of the present invention, the down converter according to the seventeenth aspect of the invention, further comprises a delay element between the third amplifier and the third mixer.
In order to accomplish this purpose, in the twentieth aspect of the present invention, the first local oscillator in the down converter according to the tenth aspect of the invention, is a fixed-frequency oscillator and the second local oscillator is a variable-frequency oscillator.